The public switched telephone network (PSTN) has evolved into an efficient real-time, multimedia communication session tool wherein users can pick up any one of nearly one billion telephones and dial any one of nearly one billion endpoints. Several developments have enabled this automated network, such as numbering plans, distributed electronic switching and routing, and networked signaling systems.
Similar to the manner in which the PSTN is based on a hierarchy, the Internet is based on an Internet protocol (IP). IP messages are routed or forwarded from one link to the next (i.e., from a source of a data flow to a destination of the data flow). Each IP packet contains an IP address, which, in Internet protocol version 4 (IPv4), for example, has 32 bits. Each IP address also has a certain number of bits dedicated to a network portion and a certain number of bits dedicated to a host portion.
IP routers are used to take a data packet from one network (or link) and place it onto another network (or link). Tables are located within IP routers that contain information or criteria used to determine a best way to route the data packet. An example of this information may be the state of network links and programmed distance indications. By using intelligent devices on both sides of a network domain, it is possible to allocate a temporary address to route a packet through a network and restore the original address on the far side of the network when the packet leaves the network. This is the basis for many current virtual private network (VPN) products and is understood in the art.
To ensure that the network elements (e.g., switches in the telephone network, routers in the data network) can perform their associated tasks, it helps for the network elements to know the status of adjacent communication links and available routes; signaling systems are used to provide this information. In telephone networks, signaling systems used are either signaling system number 7 (SS7) or are equivalent to SS7. An SS7 network is separate from a voice network and is used for the purpose of switching data messages pertaining to the business of connecting telephone calls and maintaining the signaling network. In addition, the SS7 digital signaling standard is utilized to interface the PSTN to the IP world. As is known by those skilled in the art, SS7 utilizes a message structure wherein messages travel from one network entity to another, independent of the actual voice and data to which the messages pertain. This message structure utilizes an envelope, referred to as a packet, for traversing messages.
Due to most current telecommunication endpoints receiving service through a PSTN-based system, a gateway is used to facilitate a multimedia packet flow between a packet data network and a PSTN. It should be noted that multimedia comprises voice, data, and/or discrete media. Gateways are installed at edges between data networks and voice networks, wherein the gateways are used to convert multimedia (and signaling) to ensure communication.
One specific type of gateway is the media gateway. The media gateway converts multimedia provided in one type of network to the format required in another type of network. For example, a media gateway could terminate bearer channels from a switched circuit network and media streams from a packet network (e.g., real time protocol (RTP) streams in an IP network). A media gateway may be capable of processing audio, video and T.120, alone or in any combination, and is capable of full duplex media translations. The media gateway may also play audio/video messages and perform other interactive voice response (IVR) functions, or may perform media conferencing.
There are several strategies for routing calls between gateways that are known in the art. Two of these strategies are full mesh routing and hierarchical routing. Full mesh routing is the standard method described in most of the softswitching architectures. Session initiation protocol (SIP) is the inter-softswitch signaling system because it supports an anywhere-to-anywhere signaling model. In this model, softswitches have a virtual connection to other softswitches for completing calls.
Softswitches, otherwise referred to as call agents or media gateway controllers, manage the gateways located within a network. The softswitch may use a media gateway control protocol to communicate with the gateways. Specifically, the media gateway control protocol runs between the softswitch and the gateways in a packet telephony network. Among the many functions of softswitches, softswitches control the part of a call state that pertains to connection control for media channels in a media gateway.
Gateways are expected to execute commands sent by the softswitches via use of the media gateway control protocol. Typically, these commands include the translation between audio signals and the packet network. Unfortunately, when running a network that comprises many softswitches, the owner of the network has many different points of policy management that need to be maintained to create a full mesh. Such policy management issues include assuring that each softswitch knows the IP address of each other softswitch and what telephone numbers or PSTN to which they connect. When running softswitches from multiple vendors, further management issues arise. The management issues are then more complicated due to the fact that the equipment may be managed through different interfaces.
When the number of softswitches deployed grows large, the sharing of different routes is likely. In the full mesh routing arrangement, the routing of calls may be difficult since several different egress softswitches may be full or not functioning. For example, if a carrier has thirty softswitches that can handle national long distance, and the network is running at about 50% full, then each originating softswitch will likely have to try an average of fifteen (15) separate softswitches before finding one with a non-blocked route. This search effort can be greatly reduced if a purely random distribution is implemented, however, it is assumed that some routes would be preferred over others due to cost or quality, thereby exacerbating the problem. In addition, the excessive functionality of softswitches, as is demonstrated by, for example, the excessive use of state sharing, causes a decrease in the flow of information (data and/or voice).